Silicone composition for coating textile substrates

ABSTRACT

A silicone composition and the uses thereof, particularly as a coating on an airbag for protecting the occupant of a vehicle in the event of a collision, are disclosed. The aim is to provide a silicone composition suitable for coating onto the inner surface of the airbag while significantly reducing the weight of the resulting coating layer to form a protective coating having enhance high-temperature, mechanical and substrate-adhesion properties. Said aim is achieved in that the composition is free of reinforcing mineral fillers and consists of a mixture of (1) at least one polyorganosilocane with alkenyl groups bound to the silicon; (2) at least one polyorganosiloxane with hydrogen atoms bound to the silicon; (3) a cross-linking catalyst; (4) an adhesion promoter comprising (4.1) at least one alkoxylated organosilane, (4.2) at least one epoxy-functional organosilicon compound, and (4.3) at least one metal chelate and/or metal alkoxide wherein the metal is selected from the group which consists of Ti, Zr, Ge, Li, Mn, Fe, Al and Mg; (5) at least one polyorganosiloxane resin; and (6) optionally at least one cross-linking inhibitor.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR97/01194, filed on Jul. 3, 1997.

The general field of the invention is that of cold-curing siliconecompositions, in particular those of the two-component type (RTV II),which crosslink by hydrosilylation or polyaddition in order to produce athin-film elastomer. These crosslinked compositions are, among others,suitable as a coating, for example for protection or for mechanicalreinforcement, on various substrate made of textile material, such aswoven, knitted or non-woven fibrous substrates, for example.

Such silicone coatings are generally obtained by coating the substrate,followed by curing, which proceeds by the polyaddition of unsaturated(alkenyl, e.g. Vi—Si) groups of one polyorganosiloxane onto hydrogens ofthe same or of another polyorganosiloxane.

These silicone compositions have found a major outlet in the coating offlexible—woven, knitted or non-woven—materials used for the manufactureof bags for the individual protection of the occupants of vehicles, alsocalled airbags.

For more details about airbags, reference may be made, in particular, toFrench Patent FR-A-2,668,106.

The present invention also relates to the application of the silicones,e.g. (RTV II), in the manufacture of such airbags.

Conventionally, the latter are formed from a fabric made of syntheticfibre, for example made of polyamide (Nylon)®, covered on at least oneof these sides with a layer of an elastomer of the chloroprene type. Thepresence of such a protective layer or coating is necessary because ofthe fact that the gases released by the gas generator (for example:carbon monoxide, NO_(x)) in the event of an impact are extremely hot andcontain incandescent particles capable of damaging the Nylon® bag. Theinner protective layer of elastomer must therefore be particularlyresistant to high temperatures and to mechanical stresses. It is alsoimportant that this elastomer coating be in the from of a uniform thinfilm adhering strongly to the substrate made of synthetic fabric whichforms the walls of the airbag.

In order to prevent the gases released by the gas generator from gettinginto the passenger compartment, it is important to ensure that theairbag exhibits good and constant impermeability. The elastomer coatingmust also allow this objective to be achieved, even when deposited insmall amounts.

Another constraint which is imposed on the elastomer coating is that ofthe ageing behaviour, i.e. the retention of the thermal, mechanical andadhesion properties over time. This constraint is all the more acutesince the airbags are stored in folded form in motor vehicles, beforetheir eventually life-saving expansion in the event of an accident.

As another criterion, one which is not negligible, it should be notedthat the protective coating must not cause problems with regard to themanufacture of the airbag, which is by stitching.

Silicone compositions have easily supplanted chloroprenes in thisapplication since it has turned out that the latter do notsatisfactorily meet all the specifications referred to above.Compositions which can be used for airbag applications in motor vehiclesare described, in particular, in EP-A-0,533,840 and U.S. Pat. No.5,296,298.

According to EP-A-0,553,840, these known silicone compositions contain:

(A) a polydiorganosiloxane having at least two alkenyl groups permolecule,

(B) a polyorganohydrogenosiloxane having at least two hydrogen atomslinked to the silicon in each molecule,

(C) a metal catalyst, the metal being of the platinum group,

(D) an adhesion promoter consisting of an epoxy-functional organosiliconcompound,

(E) an inorganic filler,

(F) a polyorganosiloxane resin, and

(G) optionally a compound used as a crosslinking inhibitor.

In U.S. Pat. No. 5,296,298, the aforementioned constituents (A) to (E)are again found but it should be noted that the adhesion promoter (D)consists here of the combination of an epoxy-functional organosiliconcompound with an alkoxylated silane containing, per molecule, a(meth)acryl or (meth)acryloxy group and, optionally, with an aluminiumchelate, while the inorganic filler (E) is given as being optional,although it is used in all the examples, 1 to 20, illustrating theinvention.

However, the aforementioned known silicone compositions suffer from thedrawback of not adhering sufficiently well to the polyamide fabric ofthe bag in order to guarantee optimum reliability, so very importantwith regard to road safety.

It is to the credit of the Applicant Company to have proposed inDocument EP-A-0,681,014 a solution which aims to remedy the drawbacks ofthe prior art. The problematic at the basis of the invention claimed inthis other document of the prior art is to obtain a silicone compositionwhich can be applied in particular as an airbag inner coating and which,for this purpose, has the most favourable properties in terms of, inparticular, fire and temperature resistance, mechanical properties,ageing behaviour, adhesion and surface uniformity, the adhesion tosubstrates made of textile material being most particularly desirable.The solution proposed by this invention consists in using:

a silicone coating composition of the type of those which arecold-curing (RTV) consisting of the mixture formed by:

(I) at least one polyorganosiloxane having, per molecule, at least twoC₂-C₆ alkenyl groups linked to the silicon,

(II) at least one polyorganosiloxane having, per molecule, at least twohydrogen atoms linked to the silicon,

(III) a catalytically effective amount of at least one catalyst,composed of at least one metal belonging to the platinum group,

(IV) an adhesion promoter,

(V) optionally a mineral filler,

(VI) optionally at least one crosslinking inhibitor, and

(VII) optionally at least one polyorganosiloxane resin,

in which the adhesion promoter consists exclusively of the at leastternary combination of the following ingredients:

(IV.1) at least one alkoxylated organosilane containing, per molecule,at least one C₂-C₆ alkenyl group,

(IV.2) at least one organosilicon compound which includes at least oneepoxy radical,

(IV.3) at least one metal M chelate and/or one metal alkoxide of generalformula: M(OJ)_(n), with n=the valency of M and J=a linear or branchedC₁-C₈ alkyl, M being selected from the group formed by: Ti, Zr, Ge, Li,Mn, Fe, Al and Mg.

A reinforcing filler such as a pyrogenic silica is always present in theexperimental part of Document EP-A-0,681,014.

In some applications, in particular for manufacturing airbags, forreasons of economic competitiveness it is desired to apply very thinlayers of silicone. The Applicant Company has found that coatingcompositions containing a reinforcing filler do not make it possibleeasily to obtain, using the conventional technique of the doctor-bladetype, very low add-on weights of the coating layer such as, for example,those less than the value of about 30 g/m².

One object of the present invention is to propose a novel siliconecoating composition which makes it possible to reduce the add-on weightof the coating layer without correspondingly changing the coatingtechnique or the operation of the corresponding machine.

Another object of the present invention is to provide a novel siliconecoating composition which makes it possible to obtain coatings whoseadd-on weight may easily be reduced, as required, down to a value as lowas one less than approximately 30 g/m².

Yet another object of the present invention is to provide a novelsilicone coating composition which makes it possible to obtain, comparedwith what happens with filled compositions, according to DocumentEP-A-0,681,014, having the same add-on weight, properties of the coatedsubstrate, in particular with regard to:

fire and temperature resistance, which are at the very least equivalent,

creasing and abrasion resistance (scrub test), which are improved,

tear strength, which are also improved,

thermal insulation, which are also improved.

These objects, among others, are achieved by the present invention whichconsists in selecting from all the possibilities offered in DocumentEP-A-0,681,014 the silicone coating compositions which include anadhesion promoter, containing exclusively the ingredients indicated inthat prior art, which are not filled and which necessarily contain apolyorganosiloxane resin.

More specifically, a first subject of the present invention is a coatingcomposition of the type of those which are cold-curing (RTV),characterized in that it is devoid of any reinforcing mineral filler andthat it consists of the mixture formed by:

(1) at least one polyorganosiloxane having, per molecule, at least twoC₂-C₆ alkenyl groups linked to the silicon,

(2) at least one polyorganosiloxane having, per molecule, at least twohydrogen atoms linked to the silicon,

(3) a catalytically effective amount of at least one catalyst, composedof at least one metal belonging to the platinum group,

(4) an adhesion promoter comprising exclusively:

(4.1) at least one alkoxylated organosilane containing, per molecule, atleast one C₂-C₆ alkenyl group,

(4.2) at least one organosilicon compound which includes at least oneepoxy radical,

(4.3) at least one metal M chelate and/or one metal alkoxide of generalformula: M(OJ)_(n), with n=the valency of M and J=a linear or branchedC₁-C₈ alkyl, M being selected from the group formed by: Ti, Zr, Ge, Li,Mn, Fe, Al and Mg,

(5) at least one polyorganosiloxane resin, and

(6) optionally, at least one crosslinking inhibitor.

This is a solventless composition.

In accordance with a preferred arrangement of the invention, thealkoxylated organosilane (4.1) of the promoter (4) is more particularlyselected from the substances of the following general formula:

in which:

R¹, R², R³ are hydrogen-containing or hydrocarbon radicals, which arethe same or different from each other and represent, preferably,hydrogen, a linear or branched C₁-C₄ alkyl or a phenyl optionallysubstituted with at least one C₁-C₃ alkyl,

U is a linear or branched C₁-C₄ alkylene,

W is a valency bond,

R⁴ and R⁵ are radicals, which are the same or different and represent alinear or branched C₁-C₄ alkyl,

x′=0 or 1, and

x=0 to 2, preferably 0 or 1 and even more preferably 0.

Without this being limiting, it may be considered thatvinyltrimethoxysilane is a particularly suitable compound (4.1).

With regard to the organosilicon compound (4.2), provision is madeaccording to the invention to select this:

either from the substances (4.2a) satisfying the following generalformula:

in which:

R⁶ is a linear or branched C₁-C₄ alkyl radical,

R⁷ is a linear or branched alkyl radical,

y is equal to 0, 1, 2 or 3, preferably equal to 0 or 1 and even morepreferably equal to 0,

with

Δ E and D, which are the same or different radicals, selected fromlinear or branched C₁-C₄ alkyls,

Δ z, which is equal to 0 or 1,

Δ R⁸, R⁹, R¹⁰, which are the same or different radicals, representinghydrogen or a linear or branched C₁-C₄ alkyl, hydrogen being moreparticularly preferred,

Δ R⁸ and R⁹ or R¹⁰ which may alternately constitute together, and withthe two carbons containing the epoxy, a 5-membered to 7-membered alkylring,

or from the substances (4.2b) consisting of epoxy-functionalpolydiorganosiloxanes comprising:

(i) at least one siloxyl functional unit of formula: $\begin{matrix}{X_{p}G_{q}{SiO}_{\frac{4 - {({p + q})}}{2}}} & {\text{(IV.2~~} b_{1} )}\end{matrix}$

in which:

X is the radical as defined above in the case of formula (IV.2a)

G is a monovalent hydrocarbon group, free of any action unfavourable tothe activity of the catalyst and selected, preferably, from the alkylgroups having from 1 to 8 carbon atoms inclusive, optionally substitutedby at least one halogen atom, advantageously, from methyl, ethyl, propyland 3,3,3-trifluoropropyl groups, and as well as from aryl groups, andadvantageously, from xylyl, tolyl and phenyl radicals,

p=1 or 2,

q=0, 1 or 2,

p+q=1, 2 or 3,

and (2i) optionally at least one siloxyl functional unit of formula:$\begin{matrix}{G_{r}{SiO}_{\frac{4 - r}{2}}} & {\text{(IV.2~~} b_{2} )}\end{matrix}$

in which G has the same meaning as above and r has a value of between 0and 3, for example between 1 and 3.

Compounds (4.2) are preferably epoxyalkoxymonosilanes (IV.2a)

By way of such compounds (IV.2a), mention may be made of:

3-glycidoxypropyltrimethoxysilane (GLYMO), or

3,4-epoxycyclohexylethyltrimethoxysilane.

With regard to the essential final compound (4.3) of the adhesionpromoter (4) of the (RTV) silicone composition according to theinvention, the preferred substances are those in which the metal M isselected from the following list: Ti, Zr, Ge, Li, Mn. It should beemphasized that titanium is particularly preferred. It may be combined,for example, with an alkoxy radical of the butoxy type.

According to the invention, one advantageous combination for forming theadhesion promoter is the following:

vinyltrimethoxysilane (VTMS)/3-glycidoxypropyltrimethoxysilane(GLYMO)/butyl titanate.

Quantitatively, it may be specified that the weight proportions between(4.1), (4.2) and (4.3), expressed in percentages by weight with respectto the total of the three, are as follows:

(4.1) ≧10, preferably between 15 and 70 and even more preferably between25 and 65,

(4.2) ≦90, preferably between 70 and 15 and even more preferably between65 and 25,

(4.3) ≧1, preferably between 5 and 25 and even more preferably between 8and 18,

it being understood that the sum of these proportions of (4.1), (4.2)and (4.3) is equal to 100%.

It has been possible to show that there is a correlation, on the onehand, between the adhesion performance and the structural performance ofthe silicone coating and, on the other hand, the weight ratio(4.2):(4.1). Thus, this ratio is preferably between 2:1 and 0.5:1, theratio 1:1 being more particularly preferred.

Advantageously, the adhesion promoter is present in an amount of from0.1 to 10, preferably 0.5 to 5 and even more preferably 1 to 3% byweight with respect to all of the constituents of the composition.

The composition according to the invention necessarily contains, inaddition, at least one polyorganosiloxane resin (5) containing at leastone alkenyl residue in its structure, and this resin has an alkenylgroup(s) weight content of between 0.1 and 20% by weight and preferablybetween 0.2 and 10% by weight.

These resins are well-known branched organopolysiloxane polymers oroligomers available commercially. They are in the form of solutions,preferably siloxane solutions. They have, in their structure, at leasttwo different functional units selected from those of formulaR₃SiO_(0.5) (M functional unit), R₂SiO (D functional unit), RSiO_(1.5)(T functional unit) and SiO₂ (Q functional unit), at least one of thesefunctional units being a T or Q functional unit.

The radicals R are the same or different, and are selected from linearor branched C₁-C₆ alkyl radicals and C₂-C₄ alkenyl, phenyl3,3,3-trifluoropropyl radicals. Mention may be made, for example, of: asalkyl radicals R, methyl, ethyl, isopropyl, tert-butyl and n-hexylradicals and, as alkenyl radicals R, vinyl radicals.

It should be understood that in the resins (5) of the aforementionedtype, some of the radicals R are alkenyl radicals.

As examples of branched organopolysiloxane polymers or oligomers,mention may be made of MQ resins, MDQ resins, TD resins and MDT resins,the alkenyl functional groups possibly being carried by the M, D and/orT functional units. As examples of resins which are particularly wellsuitable, mention may be made of vinyl MDQ resins having a vinyl-groupweight content of between 0.2 and 10% by weight.

This compound (5) has the function of increasing the mechanical strengthof the silicone elastomer coating, as well as its adhesion, within thecontext of coating the sides of a synthetic fabric (for example made ofpolyamide) stitched in order to form airbags. This structural resin isadvantageously present in a concentration of between 10 and 70% byweight with respect to all of the constituents of the composition,preferably between 30 and 60% by weight and even more preferably between40 and 60% by weight.

The polyorganosiloxane resin (5) will particularly preferably contain atleast 2% by weight of SiO₂ functional units (Q functional units), inparticular from 4 to 14% and preferably from 5% to 12%.

The polyorganosiloxane (1) is, weightwise, one of the main constituentsof the composition according to the invention. Advantageously, this is asubstance containing

(i) siloxyl functional units of formula: $\begin{matrix}{T_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & (1.1)\end{matrix}$

in which:

T is an alkenyl group, preferably vinyl or allyl,

Z is a monovalent hydrocarbon group, free of any action unfavourable tothe activity of the catalyst and selected, preferably, from alkyl groupshaving from 1 to 8 carbon atoms inclusive, optionally substituted by atleast one halogen atom, advantageously, from methyl, ethyl, propyl and3,3,3-trifluoropropyl groups and as well as from aryl groups and,advantageously, from xylyl, tolyl and phenyl radicals,

a is 1 or 2, b is 0, 1 or 2 and a+b is between 1 and 3, preferablybetween 2 and 3, and (2i) optionally other siloxyl functional units offormula: $\begin{matrix}{Z_{c}{SiO}_{\frac{4 - c}{2}}} & (1.2)\end{matrix}$

in which Z has the same meaning as above and c has a value of between 0and 3, preferably between 2 and 3.

It is advantageous for this polydiorganosiloxane to have a viscosity atleast equal to 1000 mPa.s and preferably between 5000 and 200,000 mPa.s.

More preferably, this viscosity will be between 10,000 and 200,000mPa.s, especially between 30,000 and 170,000, in particular between40,000 and 120,000. Of course, in the case of a mixture of several oils(1) of different viscosity, the viscosity of the mixture is taken intoaccount.

All the viscosities involved in the present document correspond to adynamic viscosity quantity which is measured, in a manner known per se,at 25° C.

The polyorganosiloxane (1) may be only formed from functional units offormula (1.1) or may contain, in addition, functional units of formula(1.2). Likewise, it may have a linear, branched, cyclic or networkstructure.

Z is generally selected from methyl, ethyl and phenyl radicals, 60 mol.% (or 60% by number) at least of the radicals Z being methyl radicals.

Examples of siloxyl functional units of formula (1.1) are thevinyldimethylsiloxyl functional unit, the vinylphenylmethylsiloxylfunctional unit, the vinylmethylsiloxyl functional unit and thevinylsiloxyl functional unit.

Examples of siloxyl functional units of formula (1.2) are SiO_(4/2),dimethylsiloxyl, methylphenylsiloxyl, diphenylsiloxyl, methylsiloxyl andphenylsiloxyl functional units.

Examples of polyorganosiloxanes (1) are linear and cyclic compounds suchas: dimethylvinylsilyl-terminated dimethylpolysiloxanes,trimethylsilyl-terminated (methylvinyl)(dimethyl)polysiloxanecopolymers, dimethylvinylsilyl-terminated(methylvinyl)(dimethyl)polysiloxane copolymers and cyclicmethylvinylpolysiloxanes.

The polyorganosiloxane (2) is preferably of the type of those whichcontain:

(i) siloxyl functional units of formula: $\begin{matrix}{H_{d}L_{e}{SiO}_{\frac{4 - {({d + e})}}{2}}} & (2.1)\end{matrix}$

in which:

L is a monovalent, hydrocarbon group, free of any action unfavourable tothe activity of the catalyst and selected, preferably, from alkyl groupshaving from 1 to 8 carbon atoms inclusive, optionally substituted by atleast one halogen atom, advantageously, from methyl, ethyl, propyl and3,3,3-trifluoropropyl groups, and as well as from aryl groups, and,advantageously, from xylyl, tolyl and phenyl radicals,

d is 1 or 2, e is 0, 1 or 2, d+e has a value of between 1 and 3,preferably between 2 and 3,

and (2i) optionally other siloxyl functional units of average formula:$\begin{matrix}{L_{g}{SiO}_{\frac{4 - g}{2}}} & (2.2)\end{matrix}$

in which L has the same meaning as above and g has a value of between 0and 3, preferably between 2 and 3.

The dynamic viscosity of this polyorganosiloxane (2) is at least equalto 10 mPa.s and preferably is between 20 and 1000 mPa.s.

The polyorganosiloxane (2) may be only formed from functional units offormula (2.1) or may contain, in addition, functional units of formula(2.2).

The polyorganosiloxane (2) may have a linear, branched, cyclic ornetwork structure.

The group L has the same meaning as the group Z above.

Examples of functional units of formula (2.1) are:

H(CH₃)₂SiO_(1/2), HCH₃SiO_(2/2), H(C₆H₅)SiO_(2/2)

Examples of functional units of formula (2.2) are the same as thosegiven above for the functional units of formula (1.2).

Examples of polyorganosiloxane (2) are linear and cyclic compounds suchas:

hydrogenodimethylsilyl-terminated dimethylpolysiloxanes,

copolymers containing trimethylsilyl-terminated(dimethyl)(hydrogenomethyl)polysiloxane functional units,

copolymers containing hydrogenodimethylsilyl-terminated(dimethyl)(hydrogenomethyl)polysiloxane functional units,

trimethylsilyl-terminated hydrogenomethylpolysiloxanes, and

cyclic hydrogenomethylpolysiloxanes.

The ratio of the number of hydrogen atoms linked to the silicon in thepolyorganosiloxane (2) to the total number of groups having alkenylunsaturation in the polyorganosiloxane (1) and in the resin (5) isbetween 0.4 and 10, preferably between 0.6 and 5.

The polyaddition silicone composition bases may contain only linearpolyorganosiloxanes (1) and (2) such as, for example, those described inPatents U.S. Pat. Nos. 3,220,972, 3,697,473 and 4,340,709, or maycontain both branched or network polyorganosiloxanes (1) and (2) suchas, for example, those described in Patents U.S. Pat. Nos. 3,284,406 and3,434,366.

Preferably, the following are employed:

at least one linear polyorganosiloxane (1) containing chains formed fromfunctional units of formula (1.2) in which c=2, these being blocked ateach of their ends by functional units of formula (1.1) in which a=1 andb=2, and

at least one linear polyorganosiloxane (2) containing in its structureat least three hydrogen atoms linked to the silicon, these being locatedin the chains and/or chain ends.

Very preferably, the following are employed:

at least one linear polyorganosiloxanes (1) containing chains formedfrom functional units of formula (1.2) in which c=2, these being blockedat each of their ends by functional units of formula (1.1) in which a=1and b=2, and

at least one linear polyorganosiloxane (2) containing chains formed fromfunctional units of formula (2.1) in which d=1 and e=1 and, optionally,functional units of formula (2.2) in which g=2, these being blocked ateach of their ends by functional units of formula (2.1) in which d=1 ande=2.

The catalysts (3) are also well-known. Preferably, platinum and rhodiumcompounds are used. In particular, it is possible to use complexes ofplatinum and of an organic substance described in Patents U.S. Pat. Nos.3,159,601, 3,159,602, 3,220,972 and European Patents EP-A-0,057,459,EP-A-0,188,978 and EP-A-0,190,530 and the complexes of platinum and ofthe vinyl organosiloxnes described in Patents U.S. Pat. No. 3,419,593,U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,377,432 and U.S. Pat. No.3,814,730. The catalyst generally preferred is platinum. In this case,the amount by weight of catalyst (3), calculated in terms of the weightof platinum metal, is generally between 2 and 400 ppm, and preferablybetween 5 and 200 ppm, these being based on the total weight of thepolyorganosiloxanes (1) and (2).

Advantageously, the silicone composition according to the invention mayalso include at least one addition-reaction retarder (6) (crosslinkinginhibitor) selected from the following compounds:

polyorganosiloxanes substituted with at least one alkenyl which mayoptionally be in cyclic form, tetramethylvinyltetrasiloxane beingparticularly preferred,

pyridine,

organic phosphines and phosphites,

unsaturated amides,

alkyl maleates, and

alkynyl alcohols.

These alkynyl alcohols (cf. FR-B-1,528,464 and FR-A-2,372,874),whichform part of the preferred thermal hydrosilylation-reaction blockers,have the formula:

R′—(R″)C(OH)—C≡CH

in which formula:

R′ is a linear or branched alkyl radical or a phenyl radical;

R″ is H or a linear or branched alkyl radical or a phenyl radical, itbeing possible for the radicals R′, R″ and the carbon atom in the αposition with respect to the triple bond optionally to form a ring;

the total number of carbon atoms contained in R′ and R″ being at least5, preferably from 9 to 20.

The said alcohols are preferably selected from those having a boilingpoint greater than 250° C. By way of examples, mention may be made of:

1-ethynyl-1-cyclohexanol;

3-methyl-1-dodecyn-3-ol;

3,7,11-trimethyl-1-dodecyn-3-ol;

1,1-diphenyl-2-propyn-1-ol;

3-ethyl-6-ethyl-1-nonyn-3-ol;

2-methyl-3-butyn-2-ol; and

3-methyl-1-pentadecyn-3-ol.

These α-alkynyl alcohols are commercially available products.

Such a retarder (6) is present in an amount of at most 3000 ppm,preferably in an amount of from 100 to 1000 ppm with respect to thetotal weight of the organopolysiloxnes (1) and (2).

In a manner known per se, one or more conventional additive(s), such ascolorants for example, may be added to the silicone elastomercomposition.

According to another of these aspects, the present invention relates toa two-component precursor system for the silicone composition describedhereinabove. Such a precursor system is in the form of two separateparts A and B, these being intended to be mixed together to form thecomposition, one of these parts A or B containing the catalyst (3) andonly one of the species, (1) or (2), of polyorganosiloxane. Anothercharacteristic of this precursor system is that its part A or Bcontaining the polyorganosiloxane (2) is free of compounds (4.3) of thepromoter (4) and that its part A or B which includes the compound (4.1)of the promoter (4) does not contain the catalyst (3). Yet anothercharacteristic of this precursor system is that the resin (5) may beemployed in part A or part B or in both parts A and B and that thecatalyst (3) must not be present in the part A or B which contains thepolyorganosiloxane (2) and the resin (5).

thus, part A may, for example, contain some of the polyorganosiloxane(1), the polyorganosiloxane (2), the compounds (4.1) and (4.2) of thepromoter (4), some of the resin (5) and, optionally, the crosslinkinginhibitor (6), while part B may, for example, contain the remaining partof the polyorganosiloxane (1), the catalyst (3), the compound (4.3) ofthe promoter (4), the remaining part of the resin (5) and, optionally, acolorant base.

The viscosity of parts A and B and of their mixture may be adjusted byvarying the amounts of the constituents and by selectingpolyorganosiloxanes of different viscosity.

Once parts A and B have been mixed together, they form a ready-to-usecomposition (RTV II) silicone, which may be applied to the substrate byany suitable coating means (for example a doctor blade or roller).

Although the composition applied to the substrate to be coated was ableto crosslink cold (i.e. at a temperature close to room temperature, =23°C.), it should be noted that the compounds according to the inventionmay also be crosslinked thermally and/or by electromagnetic radiation(electron beam).

The compositions according to the invention may be used for covering orcoating woven, knitted or non-woven fibrous substrates and, preferably,woven, knitted or non-woven substrates made of synthetic fibres,advantageously polyester or polyamide fibres.

The invention relates more particularly to the covering or coating of atleast one of the sides of the flexible substrate material (polyamidefabric, for example) used for manufacturing, by stitching, airbags forthe individual protection of the occupants of vehicles in the event ofan impact.

Within this context, the compositions according to the invention proveto be noteworthy not only for coating substrates conventionally used inmanufacturing airbags but also for coating, for this purpose, substrateshaving an open construction. Substrate having an open construction isunderstood to mean substrates having a porosity >15 l/dm²/min accordingto the DIN 53 887 standard. In the case of a fabric, the openconstruction may in particular be defined as corresponding to a numberof warp and weft yarns per centimeter, the sum of which is less than orequal to 36.

As fabrics particularly recommended within the scope of the presentinvention, mention may be made in general of fabrics whose weight in theuncoated state is less than 200 g/m² and especially less than or equalto 160 g/m². Thus, mention may be made of such fabrics, especiallypolyamide fabrics, having from 16×16 to 18×18 yarns/cm, for example 470dtex (decitex) fabrics having these characteristics.

It will be noted that it will also be possible to use substrates,especially fabrics, formed from high-performance textile fibres, that isto say textile fibres having enhanced properties with respect toconventional fibres, for example increased tenacity, so as to conferparticular or enhanced properties depending on the applications of thecoated substrate or fabric.

The Applicant Company has been able to demonstrate that the inventionallowed cold-curing elastomers to be obtained which, once crosslinked,have the following characteristic:

relative density <1.1 (this may be measured, for example, by weighing aknown volume or by picnometry or by a density-gradient column);

thermal conductivity at 23° C. (ASTM D 2326-70) ≦0.18 W/m.K;

elastic property represented by the ratio between the tensile strength(in mPa, according to 53504 standard) of the crosslinked elastomer andthe elongation at break (in %, according to the 53504 standard) of thecrosslinked elastomer, this ratio being <0.02; and

adhesion (NFG 37110), scrub ≧400.

The best performance characteristics are obtained in the case ofcompositions which contain the oil (1) having a viscosity of between10,000 and 200,000 mPa.s, especially between 30,000 and 170,000, inparticular between 40,000 and 120,000, and resin (5) containing Qfunctional units, especially at least 2% by weight of such functionalunits, in particular from 4 to 14% and preferably from 5% to 12%.

The relative density obtained by the composition according to theinvention makes it possible to produce thin-film coatings,advantageously less than or equal to 30 g/m², especially between 15 and30 g/m² and preferably about 25 g/m². The elastic property of theelastomer enables the tear strength of the coated textile to beconsiderably increased. The low thermal conductivity of the elastomergives the coated fabric first-order thermal protection, even with such alow coating thickness.

Other properties, such as pliability, adhesion of the elastomer to thefabric, gas impermeability, creasing and abrasion resistance, ageingbehavior, stitchability and stitching integrity are also of a very highlevel.

In particular, it may be pointed out that the invention makes itpossible to obtain a coated substrate exhibiting:

tear strength greater than or equal to 400 N (ASTM D 1682 standard);

thermal protection of the fabric improved by 30% compared with astandard silicone of greater relative density, for the same add-onweight; and

porosity (DIN 53 887)<2 l/dm²;min.

The subject of the invention is therefore also the use of a compositionor of its precursor system, such as those described hereinabove, forcovering or coating woven, knitted or non-woven fibrous substrates,especially those made of synthetic fibres, advantageously made ofpolyester or polyamide fibres.

According to one advantageous embodiment, the invention relates to thecoating of a fabric having an open construction, according to thedefinition given above.

The subject of the invention is therefore also such a fibrous substratecoated according to the invention and therefore able to exhibit thecharacteristics and properties indicated above.

Preferably, the fibrous support is a fabric having an open construction.Preferably, the composition contains an oil (1) having a viscosity ofbetween 10,000 and 200,000, preferably between 30,000 and 170,000, evenmore preferably between 40,000 and 120,000 mPa.a at 25° C. and a resin(5) containing Q functional units, preferably at least 2% by weight,especially from 4 to 14%, even more preferably between 5% and 12%. Alsopreferably, the add-on weight of elastomer is less than or equal to 30g/m², especially about 25 g/m². The coated substrate advantageously hasa weight of less than or equal to 200 g/m².

By virtue of the properties and characteristics indicated above, it ispossible to produce airbags for the individual protection of theoccupants of a vehicle based on fabrics having an open construction asdescribed hereinabove, in particular polyamide or polyester fabrics,which, once coated, have a weight of less than or equal to 200 g/m² andpossessing, moreover, optimum properties, especially tear resistance,thermal protection, porosity and pliability. This makes it possible toproduce airbags which are lighter, have higher performance and are lessexpensive than bags produced from uncoated fabrics or from coatedfabrics of the prior art.

The subject of the invention is also the use of a crosslinking siliconecomposition, especially of the cold- or hot-curing type, made of anelastomer having a relative density <1.1, a thermal conductivity at 23°C.≦18 W/m.K and the ratio between the tear strength and the elongationat break of which is <0.02, for coating a woven, knitted or non-wovenfibrous substrate, especially for the purpose of producing airbags forprotecting the occupants of vehicles. The invention relates here inparticular to the coating of substrates having an open constructionaccording to the definition given above, preferably with an elastomerthickness of less than or equal to 30 g/m², in particular of about 25g/m², especially so as to obtain a coated substrate having a weight ofless than or equal to 200 g/m². The invention also relates to the coatedfibrous substrates thus obtained.

The invention relates in particular to the covering or coating of atleast one of the sides of the flexible substrate material (polyamidefabric, for example) used for manufacturing, by stitching, airbags forthe individual protection of the occupants of vehicles in the event ofan impact.

However, it is well understood that the invention is not limited therebyand it may be employed in any application requiring similar properties.Mention may be made, for example, of tent fabrics, parachute fabrics andthe like which could also draw benefit from some of the abovementionedproperties, allied with lightness.

In general, the coating involved here may correspond to depositing asingle layer on at least one of the sides of the flexible substratematerial (primary coat). However, it may also involve depositing asecond layer or optionally a third layer on at least one of the sides ofthe substrate material already coated (secondary coat) in order to havein total the desired thickness which guarantees the best possibleperformance characteristics in terms of impermenability.

The following examples, of preparation of the composition and of itsapplication as a covering for a polyamide fabric, will enable theinvention to be more clearly understood and will enable its advantagesand its alternative embodiments to be apparent. The performancecharacteristics of the composition of the invention will be demonstratedbelow by comparative tests.

EXAMPLES

In these examples, the viscosity is measured using a RROOKFIELDviscometer according to the information in the AFNOR NFT 76 106 standardof May 1982.

Example 1

Example of the preparation of compositions

1. Preparation of an unfilled silicone composition according to theinvention (composition C1)

1.1 Preparation of part A of the two-component system

The following are mixed in a reactor, at room temperature

48 parts by weight of resin (5) having a MN^(Vi)DD^(Vi)Q structurecontaining 0.6% by weight of vinyl groups (Vi) and consisting of 17% byweight of (CH₃)₃SiO_(0.5) functional units, 0.5% by weight of(CH₃)₂ViSiO_(0.5) functional units, 75% by weight of (CH₃)₂SiOfunctional units, 1.5% by weight of (CH₃)ViSiO functional units and 6%by weight of SiO₂ functional units [this constituent being called resin(5) hereinafter];

30 parts by weight of a polyorganosiloxane (1) consisting of apolydimethylsiloxane oil terminated at each of the chain ends by a(CH₃)₂ViSiO_(0.5) functional unit, having a viscosity of 100,000 mPa.sand containing 0.003 Vi-Si functional groups per 100 g of oil [thisconstituent being called hereafter high-viscosity oil (1)];

15 parts by weight of a polyorganosiloxane (1) consisting of apolydimethylsiloxane oil terminated at each of the chain ends by a(CH₃)₂ViSiO_(0.5) functional unit, having a viscosity of 10,000 mPa.sand containing 0.005 Vi-Si residues per 100 g of oil [this constituentbeing called hereafter low-viscosity oil (1)];

5 parts by weight of a polyorganosiloxane (2) consisting of apoly(dimethyl)(hydrogenomethyl)siloxane oil terminated at each of thechain ends by a (CH₃)₂HSiO_(0.5) functional unit, having a viscosity of25 mPa.s and containing in total 0.7 H-Si functional groups per 100 g ofoil (of which 0.6 H-Si functional groups lie within the chain) [thisconstituent being called hereafter oil (2)];

0.025 parts by weight of inhibitor (6) consisting of ethylcyclohexaol[this constituent being called hereafter inhibitor (6)];

1 parts by weight of compound (4.1) of the promoter (4), consisting ofvinyltrimethoxysilane [this constituent being called hereafter VTMS(4.1)];

and 1 parts by weight of compound (4.2) of the promoter (4), consistingof 3-glycidoxypropyltrimethoxysilane [this constituent being calledhereafter GLYMO (4.2)].

1.2 Preparation of part B of the two-component system

The following are mixed in a reactor at room temperature:

44.6 parts by weight of resin (5);

36.3 parts by weight of high-viscosity oil (1);

14.5 parts by weight of low-viscosity oil (1);

0.6 parts by weight of a colorant base, based on bromophthal bluereferenced 4 GP, sold by the company CIBA GEIGY [this constituent beingcalled hereinafter colorant base];

0.0215 parts by weight of platinum metal, introduced in the form of anorganometallic complex containing 12% by weight of platinum metal, knownby the name Earstedt catalyst [this constituent being called hereafterplatinum of the catalyst (3)]; and

4 parts by weight of compound (4.3) of the promoter (4), consisting ofbutyl titanate Ti(OBu)₄ [this constituent being called hereafterTi(OBu)₄ (4.3)].

1.3 Preparation of the two-component system

The two-components system is obtained by mixing, at room temperature,100 parts by weight of part A and 10 parts by weight of part B.Composition C1 is thus obtained, the proportions of the constituents ofwhich are indicated in Table I given below.

2. Preparation of a filled silicone composition acting as the controlcomposition (composition C2)

2.1 Preparation of a primary coating material

The following are introduced into a planetary mixer:

35 parts by weight of resin (5);

29 parts by weight of ground quartz having an average particle size ofabout 2.5 μm and developing a BET surface area of about 3 m²/g, acid bythe company SIFRACO [this constituent being called hereafter filler No.1];

23.2 parts by weight of high-viscosity oil (1);

11.8 parts by weight of low-viscosity oil (1); and

1 part by weight of pyrogenic silica treated withoctamethylcyclotetrasiloxane and developing a BET surface area of about250 m²/g [this constituent being called hereafter filler No. 2].

2.2 Preparation of part A of the two-component system

The following are mixed in a reactor at room temperature:

94 parts by weight of the above coating material;

4 parts by weight of oil (2);

0.025 parts by weight of inhibitor (6);

1 parts by weight of VTMS (4.1); and

1 part by weight of GLYMO (4.2).

2.3 Preparation of part B of the two-component system

The following are mixed in a reactor at room temperature:

88.3 parts by weight of the above coating material;

7.6 parts by eight of high-viscosity oil (1);

0.1 part by weight of colorant base;

0.0215 parts by weight of platinum of the catalyst (3); and

4 parts by weight of Ti(OBu)₄ (4.3).

2.4 Preparation of the two-component system

The two-component system is obtained by mixing, at room temperature, 100parts by weight of part A and 10 parts by weight of part B. The controlcomposition C2 is thus obtained, the proportions of the constituents ofwhich are indicated in Table I given below.

TABLE I Compositions (parts by weight) C1 C2 Resin (5) 47.68  32.71 High-viscosity oil (1) 30.56  22.37  Low-viscosity oil (1) 14.96  11.02 Oil (2) 4.54  3.63  Inhibitor (6) 0.023 0.023 Colorant base 0.055 0.009Platinum of the catalyst (3) 0.002 0.002 VTMS (4.1) 0.91  0.91  GLYMO(4.2) 0.91  0.91  Ti(OBu)₄ (4.3) 0.36  0.36  Fillers No. 1 and No. 2 —28.06  Total 100.00   100.00  

Example 2

Example of an application as a covering for a polyamide fabric

1. Application protocol

The composition is deposited using doctor blades on fabrics based onnylon-6,6-type polyamide (polyhexamethyleneadipamide) having lineardensities in decitex (dtex) which very and then, after coating, it iscrosslinked, each time for 4 minutes at 150° C. in an oven sold by thecompany MATTHIS.

2. Results

2.1 Coating on a desired polyamide fabric of 235 dtex having 28.5×28.5yarns/cm, and evaluation of the saving obtained, with regard toreduction in the add-on weight of the coating layer for the same settingof the coating blade and going from the control composition to thecomposition according to the invention:

TABLE II Saving in Fire Scrub test Add-on add-on resistance (numberweight weight (mm/min) of scrubs) Composition (g/m²) (%) (1) (2) C2 31 —75  500 C1 25 20 85 1000 (1) The measurements are carried out accordingto the information in the FMVSS 302 standard (“Flammability MotorVehicle Safety Standard”). (2) The creasing and abrasion resistance test(scrub test) (NF G 37110 standard) reflects the adhesion and ageingbehaviour of the composition. This test consists in subjecting thefabric, on the one hand, to a shearing movement by means of two jawswhich grip the two opposite edges of a test piece and which perform ato-and-fro motion one with respect to the other and, on the other hand,to abrasion by contact with a movable support.

2.2 Coating on a desired polyamide fabric of 470 dtex having 18×18yarns/cm, i.e. a fabric having an open construction (porosity <15l/dm²/min), and evaluation of the fire resistance and the scrub test ongoing from the control composition to the composition according to theinvention, for the same add-on weight of the coating layer

TABLE III Fire Scrub test Add-on resistance (number weight (mm/min) ofscrubs) Composition (g/m²) (1) (2) C2 32 60  300 C1 32 57 1000 (1) and(2), cf. the information given above in Table II

2.3 Coating on a desired polyamide fabric of 470 dtex having 18×18yarns/cm (open construction) and evaluation of the mechanical propertieson the coated fabric on going from the control composition to thecomposition according to the invention

TABLE IV Add-on Tear weight resistance Composition (g/m²) (1) (N) C2 32300 C1 33 420 (1) The measurements are carried out according to theinformation in ASTM D 1682 standard.

2.4 The thermal conductivity of the solid silicone elastomers, preparedby crosslinking the compositions C1 and C2 at 150° C., was measured attwo different temperatures according to the information in the ASTM D2326-70 standard. The ratio between the tear strength [TS, in MPa] ofthe crosslinked elastomer and its elongation at break [E_(b), in %] hasalso been measured [TS and Eb are evaluated according to the informationin the DIN 53504 standard]

TABLE V Thermal conductivity (W/m.K) Relative TS/E_(b) Composition at23° C. at 170° C. density ratio C2 0.23 0.21 1.2  0.03  C1 0.17 0.141.05 0.015

When the coated fabrics having the same thickness of compositions C1 andC2 are exposed to a high temperature, the protection afforded bycomposition C1 according to the invention is superior.

2.5 Coating on a desired polyamide fabric of 470 dtex having 16×16yarns/cm (open construction) using composition C1 and a composition C3defined below.

2.5.1 Composition C3

Part A of the two-component system:

The same as for part A in C1 except for the components (5) and (1) whichbecome:

48 parts by weight of resin (5) having a MM^(Vi)DD^(Vi)Q structurecontaining 0.8% by weight of vinyl groups (Vi) and consisting of 27% byweight of (CH₃)₃SiO_(0.5) functional units, 0.15% by weight of(CH₃)₂ViSiO_(0.5) functional units, 60% by weight of (CH₃)₂SiOfunctional units, 2.4% by weight of (CH₃)ViSiO functional units and 9.6%by weight of SiO₂ functional units;

45 parts by weight of an organopolysiloxane (1) consisting of apolydimethylsiloxane oil terminated at each of the chain ends by a(CH₃)₂ViSiO_(0.5) functional unit, having a viscosity of 100,000 mPa.sand containing 0.003 Vi-Si functional groups per 100 g of oil.

Part B of the component:

The same as for part B in C1 except for components (5) and (1) whichbecome:

45 parts by weight of resin (5) as described in A;

51 parts by weight of oil (1) as described in A.

Preparation of the two-component system:

The same as C1.

2.5.2 Characteristics of the fabric and the coating

uncoated fabric weight: 160 g/m²;

silicone add-on weight: 30 g/m².

2.5.3 Results

Properties of the crosslinked elastomer:

conductivity at 23° C. (ASTM D 2326-70 standard): 0.17 W/m.K for C1 andC3;

elongation at break (DIN 53504): 190% for C1; 250% for C3;

tear strength (ASTM D 624): 3 kN/m for C1; 9 kN/m for C3.

Properties of the coated fabric:

tear strength (DIN ASTM D 1682):

fabric alone: 100 N;

coated fabric: 450 N for C1 and C3.

creasing resistance at 30 g/m² (NF G 37110):

800-1000 for C1;

1500-1700 for C3.

2.6 Coating on a desired polyamide fabric of 470 dtex and with 21×20yarns/cm, coated to 25 g/m² using composition C1 and composition C3

tear strength (ASTM D 1682):

fabric alone: 210 N;

fabric coated with C1: 550 N;

fabric coated with C3: 520 N.

pliability (ASTM D 4032-94):

fabric coated with C1: 15;

fabric coated with C3: 9.

This pliability test reflects the flexibility of the fabric and itscapacity to be folded up into a small volume (the lower the value, thebetter the pliability).

What is claimed is:
 1. A coating composition, characterized in that itis devoid of any reinforcing mineral filler and that it consists of themixture formed by: (1) at least one polyorganosiloxane oil having, permolecular, at least two C₂-C₆ alkenyl groups linked to the silicon, (2)at least one polyorganosiloxane having, per molecule, at least twohydrogen atoms linked to the silicon, (3) a catalytically effectiveamount of at least one catalyst, composed of at least one metalbelonging to the platinum group, (4) an adhesion promoter comprisingexclusively, (4.1) at least one alkoxylated organosilane containing, permolecule, at least one C₂-C₆ alkenyl group, (4.2) at least oneorganosilicon compound which includes at least one epoxy radical, (4.3)at least one metal M chelate and/or one metal alkoxide of generalformula: M(OJ)n, with n=the valency of M and J=a linear or branchedC1-C8 alkyl, M being selected from the group formed by: T, Zr, Ge, Li,Mn, Fe, Al and Mg, (5) at least one vinyl MQ or a vinyl MDQ resin,containing in its structure from 0.1 to 20% by weight of an alkenylgroup or groups, having a vinyl-group weight content of between 0.2 and10% by weight, and from 4 to 14% by weight of Q functional units, saidresin being in a concentration of between 10 and 70% by weight withrespect to all the constituents of the composition, and (6) optionally,at least one crosslinking inhibitor.
 2. Composition according to claim1, characterized in that the vinyl MQ or the vinyl MDQ resin presentsfrom 5 to 12% by weight of Q functional units, said resin being in aconcentration of between 30 and 60% by weight respect to all theconstituents of the composition.
 3. A process for coating a woven,knitted or non-woven fibrous substrate comprising the step of coatingsaid woven, knitted or non-woven fibrous substrate with a composition asdefined in claim
 1. 4. A process according to claim 3, wherein saidwoven, knitted or non-woven fibrous substrate forms airbags forprotecting the occupants of vehicles.